manifestmerge: have manifest do matching before diffing

This means that the diff code does less work, potentially
significantly less in the case of treemanifests. It also should ease
implementation with narrowed clone cases (such as narrowhg) when we
don't always have the entire set of treemanifest revlogs locally.

As far as I can tell, this codepath is currently only used by record,
so it'll probably die in the near future, and then narrowhg won't have
to worry about composing with some unknown matching system.

mercurial/merge.py

@@ -722,12 +722,13 b' def manifestmerge(repo, wctx, p2, pa, br'
                 break
 
     # Compare manifests
+    if matcher is not None:
+        m1 = m1.matches(matcher)
+        m2 = m2.matches(matcher)
     diff = m1.diff(m2)
 
     actions = {}
     for f, ((n1, fl1), (n2, fl2)) in diff.iteritems():
-        if matcher and not matcher(f):
-            continue
         if n1 and n2: # file exists on both local and remote side
             if f not in ma:
                 fa = copy.get(f, None)